Radar system providing plan position indicator and elevation views



Aug. l5, 1950 INDICATOR ANDiELEVATION VIEWS Filed March 27, 1946 l. WOLFF RADAR SYSTEM PROVIDING PLN POSITION Patented Aug. 15, 1950 RADAR SYSTEM PROVIDING PLAN POSI- TION INDICATOR AND ELEVATION Irving wom, Princeton, N. J., assigner tnaan Corporation ware.4 .Y

of America, a corporation of DeineA Application March 27, 1946, Serial No. 657,419

Claims.`

My invention relates to pulse-echo radar or radio locator systems and particularly to systems for obtaining three dimensional information.

An object of the invention is to provide an improved method of and means for obtaining information as to distance. azimuth and elevation of aircraft.

A further object oi the invention is toprovide an improved radar system of the plan-positionindicator or P. P. I. type which gives elevation information in addition to the distance and azimuth information.

According to a preferred embodiment of the invention, radio pulses are radiated from a directional antenna that is rotated in azimuth at a comparatively slow rate while it is tilted in elevation at a comparatively fast rate. The reflected pulses are supplied to the control grid of a cathode ray tube on which the P. P. I. indication is to appear. The cathode ray of the tube is deilected radially in synchronism with the pulse transmission by means of a. deilecting yoke that is rotated in synchronism with the rotation i of the antenna in azimuth. Thus a P. P. I. view is produced on the screen end of the cathode ray tube, the plan position of a -pulse reecting aircraft being shown by a spot on a phosphorescent screen which is of the short persistence type.

In order to obtain information as to the height of the aircraft, a partially reilecting and partially transmitting mirror such as a half-silvered mirror or the like is supported above the screen end of the cathode ray tube so that it may be vrotated with the deflecting yoke and simultaneously tilted in svnchronism with the tilting ci the antenna in elevation. Thus, looking at the mirror from the side, a spot on the tube screen will appear to be at a height or elevation dependside view showing aircraft elevation is provided by the tilting mirror and the fast persistence screen. The invention will be better understood from with the accompanying drawing in which the single figure is a block diagram and perspective view showing one embodiment of the invention.

The drawing shows a pulse-echo radar system comprising a radio pulse transmitter I0 that supplies radio pulses through an antenna duplexer or T-R box Il to a directive antenna I2 from which the pulses are radiated. In the example shown, the antenna I2 is a dipole which `is mounted in a parabolic reflector I3. The T-R box may be of the type described, for example. in application Serial No. 491,963, led June ,23,

\1943, and entitled Radio Transmitter-Receiver Automatic Switching System, now Patent No. 2,412,315, issued December 10, 1946, or in Wireless World for December 1945, page 304.

Any pulses reflected by aircraft are picked up by the antenna. I2 and supplied through the T-R box II to a receiver I4. Demodulated or video frequency pulses are supplied from the receiver I4 to the control grid I6 of a cathode ray tube I1.

The antenna I2 is rotated in azimuth about a vertical axis I8 by means of a motor I9. The cathode ray tube I1 is provided with a defiecting yoke 2| which is rotated by means of the motor I9 in synchronism with the rotation of the antenna in azimuth.

A sawtooth wave deilecting circuit 22, which is synchronized with the pulse transmission, supplies sawtooth current to the defiecting yoke 2l through slip rings 23. Thus, the cathode ray is deiiected radially from the center of the cathode ray tube as the yoke 2l is rotated. 'Ihe system thus far described would produce the usual P. P. I. picture or imageon a phosphorescent screen 24 on the end oi' the tube I1 except for the fact that the screen 24 is made to have short persistence for a reason that will become apparent. Such a screen is made of short decay time iluorescent material. In order to obtain a full 360 degree P. P. I. image that is visible at one time, the information appearing on the screen 24 is projected by a lens system 26 upon a long persistence screen 21. Such a screen is made of long decay time fluorescent material. In this way the customary P. P, I. picture may be viewed on the screen 21. Merely by way of example, it may be mentioned that the short persistence screen 24 may be a blue-light emitting screen of the composition ZnS:Ag(.01) and the long .persistence screen 21 may be a yellow-light the following description taken in connection emitting meen 0f the imposition The antenna I2 may be tilted up and down at avcomparatively rapid rate about an axis 28 by means of a reversible motor 29. The motor 29 is supplied with power from a battery 3l through a limit switch 32 that reverses the polarity of the power supply to the motor at the upper limit of antenna tilt and at the lower limit of antenna tilt. In the example shown, the switch 32 comprises a fork portion 33 that is slidably mounted in a supporting member 34. As the shaft 29 rotates to a limit position, a pin 36 moves the fork 33 into engagement with one switch contact point and out of engagement with the other switch contact point.

A partially reflecting and partially transmitting mirror 31 is supported above the short persistence screen 24 soll that it may be tilted between a Vvertical position and a position of 45 degrees with respect to the screen 24. The mirror 31 is tilted in synchronism with the tilting of the antenna I2 by means of Seisyn motors 38 and 39, for example. The motor 38 is coupled to the shaft 28 -while the motor 39 is coupled through gears 40 and 4| to the pivot shaft 45 of the mirror 31. The pivot shaft 45 passes through or intersects the longitudinal axis of the tube I1.

Both the mirror. 3l and the Seisyn motor 39 may be supported by means of a ring 42 of insulating material which is rotatably mounted on bearing blocks 43. Current from the Seisyn motor 38 is supplied over conductors 44 and through brushes 46 and slip rings 41 to the Seisyn motor 39.

When the antenna I2 is tilted to its position of maximum elevation, the mirror 31 is tilted to its 45 degree position. If at this time there is an aircraft in the path of the radio beam so that a spot is produced on the screen 24, this spot as seen in the mirror when viewed from the side will appear to be at a maximum altitude. Preferably the mirror 31 is tilted at a rate at least equal to persistence of vision but this is not essential.

While the' mirror 31 is being tilted rapidly, it is also being rotated comparatively slowly in synchronism with the rotation of the antenna I2 and the deilecting yoke 2l. This may be accomplished by driving the supporting ring 42 by the motor I9 through gears 5I and 52.

In using the equipment for detecting the approach of enemy aircraft, for example, several observers may watch the screens. One observer may watch the P. P. I. picture on the screen 21 while two or more observers may be stationed around the cathode ray tube I1 to watch the elevation view in the mirror 31 as it rotates slowly into position for each elevation observer.

The invention is not limited to a system employing a radar system of the pulse-echo type. If desired a frequency modulated or FM type of radar system, for example, may be employed. A method by which distance .information may be obtained by an FM radar system is described and claimed in my copending application Serial No. 452,990, filed July 31, 1942, and entitled Distance Measuring Apparatus, now Patent No. 2,422,157, issued June 10, 1947.

I claim as my invention:

1. A radio locator system comprising a directive 'ill electron gun for directing an electron beam against said screen and also having a control electrode for causing said electron beam to produce an indication in response to a signal being applied to said control electrode, means for receiving and demodulating said radio energy after reflection and for then applying the resulting signal to said control electrode, means for deecting said electron beam along a time axis, a long persistence luminescent screen and means for projecting thereupon the view produced on said short persistence screen whereby a picture containing distance information may be viewed on said long persistence screen, a partially reflecting and partially transmitting mirror pivotally mounted adjacent to said short persistence screen, and means for tilting said mirror about its pivot axis in synchronism Awith said scanning in elevation. Y

2. A pulse-echo radio locator system comprising Y a directive antenna having a directional radiation pattern, means for radiating radio pulses from said antenna. means for scanning in elevation with said radiation, a cathode ray indicator tube having a short persistence luminescent screen and an electron gun for directing an electron beam against said screen and also having a control electrode for causing said electron beam to produce an indication'in response to a pulse being applied to said control electrode, means for receiving and demodulating said radio pulses after reflection and for then applying them to said control electrode, means for deilecting said electron beam in synchronism with the radiation of said pulses, a long persistence luminescent screen and means for projecting thereupon the view produced on said short persistence screen whereby a picture containing distance information may be viewed on said long persistence screen, a partially reflecting and partially transmitting mirror pivotally mounted adjacent to said short persistence screen with the pivot axis of the mirror adjacent to the screen, and means for tnt-mg said mirror about its pivot axis in synchronism with said scanning in elevation and with the tilting of the mirror lying between the limits of degrees and 45 degrees with respect to the fast persistence screen.

3. A pulse-echo radio locator system comprising a directive antenna having a conical or pencillike radiation pattern, means for radiating radio pulses from'said antenna, means for scanning in azimuth with the radiation from said antenna at a comparatively slow rate, means for simultaneously scanning in elevation with said radiation at a comparatively fast rate, a cathode ray indicator tube having a short persistence luminescent screen and an electron gun for directing an electron beam against said screen and also having a control electrode for modulating the intensity of said electron beam, meam for receiving and demodulating said radio pulses after reflection and for then applying them to said control electrode, means for providing a'deflecting field for deflecting said electron beam radially in synchronism with the radiation of said pulses, means for rotating said deilecting field in synchronism with said scanning in azimuth, a long persistence luminescent screen and means for projecting thereupon the view produced on said short persistence screen whereby a picture containing distance and azimuth information may be viewed on said long persistence screen, a partially reflecting and partially Iu'ansmitting mirror pivotally mounted adjacent to said short persistem screen with the pivot axis of said minor l adjacent to the screen and intersecting the longitudinal axis o! the cathode ray tube, means for rotating said mirror about said longitudinal axis and in synchronism with said scanning in azimuth, and means for tilting said mirror about its pivot axis in synchronism with said scanning in elevation and with the tilting of the mirror lying between the limits of 90 degrees and 45 degrees with respect to the fast persistence screen.

4. A pulse-echo radio locator system comprising a directive antenna having a conical or pencillike radiation pattern, means for radiating radio pulses from said antenna, means for rotating said radiation pattern in azimuth, at a comparatively slow rate, means for simultaneously tilting said radiation pattern in elevationat a comparatively fast rate, Aa cathode ray indicator tube having a short persistence luminescent screen and an elec trongun for directing an electron beam against said screen and also having a control electrode for modulating the intensity oi' said electron beam, means for receiving and demodulating said radio ,pulses after reflection and for then applying them to said control electrode, means for providing a deilecting field for deiiecting said electron beamradially in synchronism with the radiation of said pulses, means for rotating said deiiecting iield in synchronism with said rotation of the radiation `pattern, a long persistence luminescent screen and means for projecting thereupon the view produced on mid short persistence screen whereby' a P. P. I. picture may be viewed on said long persistence screen. a 'partially reilecting and partialy transmitting mirror pivotally mounted adjacent to said tween the limits of 90 degrees and 45 degrees with m `the fast persistence screen.

5. A radio locator system comprising a directive antenna having a directional radiation pattern. means for radiating radio energy from said an- ;tenna, means for scanning along one coordinate ,sponse to a signal being applied to said control electrode, means for receiving "said radio energy after reiiection and for then applying the rreceived signal to saidcontrol electrode, ineens for deect- -ing said electron beam along Vatime axis and for :also deilecting said electron beam in synchronism -with said slow scan whereby indications of all refiiecting objects in the iield of scan of said antenna ,appear on said short persistence screen, a long persistence luminescent screen and means for projecting thereupon the view produced on said short persistence screen whereby there appears on said long persistence screen an indication of the posi- Ation of each reilecting object in terms of distance from the transmitter and in terms of the coordinate of the slow scan, means comprising an optical system `that is synchronized with said fast 'scan for selecting a section ofthe slow scan and ,for producing an indication of the position of each reflecting object in terms of @distance .from the transmitter and in terms of the coordinate of the Vfast scan.

IRVING WOLFF.

ntmsnENcEs crrnn The following references are of record in the le oi this patent:

UNITED lSTATES PATENTS ,Number Name Date 2,408,848 Hammond oct. s, 1946 22,409,456 Toison et a1 Oct, 15, 1946 

